the science in sSid eKIN
AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE
Dear Reader:
Science data and statistics are always changing, and it is important to be informed of current research. To help keep you up-to-date with the latest information on skin health, the American Association for the Advancement of Science would like to share the following updates regarding skin health:
N Major medical groups, including the CDC, recommend using sunscreen with an SPF of 15 or higher. However, a growing number of health care providers, including the M.D. Anderson Cancer Center, suggest products of SPF 30 or higher, particularly for those whose
skin burns easily. (See references on pages 17, 32, and 45.)
N The number of doctor visits Americans make each year to get skin rashes checked out has dropped from 11.8 million to 10 million, according to the National Ambulatory Medical Care Survey: 2006 Summary, National Health Statistics Report No. 3. (See reference
on page 23.) http://www.cdc.gov/nchs/data/nhsr/nhsr003.pdf is
the most recent data. Check the site for regular updates to the statistics.
N According to the CDC’s National Program of Cancer Registries,
53,792 new cases of melanoma were reported in 2005, the most recent year for which statistics were available in Summer 2009. The National Cancer Institute estimates that 68,720 new cases
will be diagnosed in 2009. (See reference on page 36.)
N Estimates vary as to the likelihood of developing melanoma during the average American’s lifetime. MedlinePlus, developed by the National Institutes of Health, estimates that 1 in 65 people will be diagnosed with melanoma at some point in their life. In 2009, The Skin Cancer Foundation predicted that 1 in 55 people will be
diagnosed. (See reference on page 36.)
As the science advances it is possible that more recent data will provide you with different numbers. While you can use this book as a starting point, check credible sites, such as those above, for results on the most up-to-date research.
the science in sSid eKIN
AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE
Published 2009 by The American Association for the Advancement of Science (AAAS) 1200 New York Avenue, NW Washington, DC 20005
© Copyright 2009 by AAAS 978-0-87168-713-5 All rights reserved. Permission to reproduce this document for not-for-profit educa- tional purposes or for use in a review is hereby granted. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form, or by any means, electronic, mechanical, photocopy, recording, or otherwise, for commercial purposes without prior permission of AAAS.
This publication was made possible by a grant from Neutrogena. Any interpretations and conclusions contained in this booklet are those of the authors and do not represent the views of the AAAS Board of Directors, the Council of AAAS, or its membership, or of Neutrogena.
T A B L E O F C O N T E N T S
INTRODUCTION: HEALTHY SKIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
PART 1: SKIN FORM AND FUNCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
What is skin? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Why do we have skin? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
PART 2: HEALTHY SKIN. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
A lifetime of skin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Babies’ skin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Teenagers’ skin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Adults’ skin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Healthy Hair and Nails . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Hair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Nails . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
PART 3: SKIN DISORDERS AND TREATMENT. . . . . . . . . . . . . . . . . . . . . . 23
Skin Allergies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Eczema. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Contact dermatitis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Hives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Psoriasis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Acne . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
PART 4: SUN EXPOSURE AND SKIN CANCER . . . . . . . . . . . . . . . . . . . . . 31
Sun and your skin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 What is skin cancer? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
PART 5: PROMISING RESEARCH: THE SKIN CARE OF TOMORROW. . . . 39
The basics of skin growth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 The genetics of skin diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Psoriasis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Skin cancer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Acne . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 The important role of volunteers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
CONCLUSION: WHAT YOU CAN DO TO HAVE HEALTHIER SKIN . . . . . . 45 APPENDIX 1: QUESTIONS TO ASK YOUR DOCTOR
ABOUT YOUR SKIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
APPENDIX 2: TAKING PART IN RESEARCH STUDIES—
QUESTIONS TO ASK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
APPENDIX 3: OTHER SKIN CONDITIONS . . . . . . . . . . . . . . . . . . . . . . . . . 51 RESOURCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
GLOSSARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 ACKNOWLEDGEMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 PHOTO CREDITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
INTRODUCTION: HEALTHY SKIN
kin is the body’s largest organ. It is also the most
S
visible. A square inch of skin has millions of cells and many nerve endings for sensing temperature, pain, pressure, and touch. It keeps us sheltered from the elements and protects our insides from drying up.
Yet despite its toughness, skin is sensitive and can be damaged if it isn’t cared for. It requires our protection from the sun and from irritants. It needs our help in retaining moisture. It demands a little thought now and then.
In this book, you will learn all about your skin and how to take care of it. You will learn about skin ailments, from acne to skin cancer, and how to prevent them. Finally, we will look at the promising research scientists are doing to improve skin care to keep your skin
The body sheds 30,000–40,000 dead skin cells off its surface every minute.
This amounts to nine pounds of cells every yea r .
healthy for a lifetime.
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S k i n : T h e S c i e n c e I n s i d e
Your skin is about 1/10 of an inch deep. The thinnest skin on your body is on your eyelids and on the inside of your elbows, and the thickest skin is on your palms, the soles of your feet, and your upper back.
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Part 1: Skin Form and Function
HAIR
PORE
EPIDERMIS
DERMIS
NERVES
FATTY OR SUBCUTANEOUS TISSUE
OIL GLAND
BLOOD VESSELS
HAIR FOLLICLE
SWEAT GLAND
A cross section of the three layers of skin
dermis mostly builds new skin
cells and makes melanin, a pigment that gives skin its
color. When we go outside, the melanin in our skin helps protect us from being burned by the sun’s ultraviolet rays.
What is skin?
Skin is actually made up of three different layers: • The epidermis • The dermis • The subcutaneous tissue
The epidermis is the top layer
of skin, the part you see. Only as thick as a sheet of paper, the epi-
Basal cells form the bottom of
the epidermis. They divide and
form squamous cells, which
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S k i n : T h e S c i e n c e I n s i d e
produce keratin, a protein that reinforces your skin cells to help protect you from the environment. of your immune system, are also found in the basal layer of your epidermis.
As the basal cells divide, they push the squamous cells up toward the surface of your skin. As they move up, the cells shrink, flatten, and die. When they reach the top layer of the epidermis, they become the
stratum corneum, the outermost
layer of skin that protects the body.
The dermis is the middle layer of our skin and makes up the majority of it. It includes strong fibers
called collagen and elastin,
which give our skin strength and elasticity.
The dermis contains sweat
glands, oil glands, blood vessels,
nerve fibers, lymphatic channels (the tubes that carry the bodily
fluid lymph), hair follicles, and
muscle cells.
Melanocytes, which make the
melanin in your skin, and
Langerhans cells, which are part
A cross section of dermal and epidermal skin layers
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Part 1: Skin Form and Function
Why are there different skin/hair colors?
- main determining factor in what color a
- No one can deny the importance of skin
color within our society. Socially it can affect many things, but scientifically, skin color is a lot less complex. person’s skin will be, there is also another pigment located in the dermis, which contributes to the color. This yellow-colored pigment, called carotene, is coverted to vitamin A. Along with the pigments, there are other factors that contribute to
skin color, such as the subcutaneous, or
fatty, tissue layer of skin. The way that light filters through this layer, as well as the other two layers of skin, has an effect on the way that skin color is perceived.
Most scientists agree that sunlight levels determine whether a population tends to have light skin or dark skin. Sunlight contains ultraviolet radiation (UV). The darker the skin, the less UV penetrates into it.
Too much UV is bad, because it destroys an important nutrient, called folate. But some UV on our skin is good, because it helps our cells produce vitamin D, another important nutrient.
Sometimes skin color develops unusually. Most people have moles (also known as birthmarks or nevi). Generally these are just harmless clusters of darkly pigmented cells, but they should be watched because changes can warn of developing skin cancer. Vitiligo is an autoimmune disease that causes the skin to develop milkywhite patches. These develop because the body mistakenly makes antibodies to its own melanin.
Where there is a lot of direct sunlight, like in places close to the equator, people get more than enough sunlight to produce vitamin D, but they are very susceptible to folate damage. Having dark skin that protects against the destruction of folate is advantageous in these parts of the world. As a result, people with genes for dark skin are healthier and produce more offspring, who also have darker skin. After many generations, populations in these areas are mostly dark-skinned.
Hair color is also a result of how much melanin a person has in their body. Individual hair shafts grow from follicles that are rooted in the subcutaneous layer, passing through the dermis and epidermis. Each hair is genetically programmed to produce a certain amount of melanin. The production of melanin occurs in the middle layer of the hair shaft, referred to as the
cortex. When hair grays,
the cortex has slowed the amount of melanin produced by the hair, causing the hair to turn gray and eventually white.
Where sunlight is weak, making it difficult to produce enough vitamin D, the genes that produce light skin are favored, allowing more UV to penetrate. In these parts of the world, people with those genes are healthier and produce more offspring. Over time, populations in these areas evolve to be light-skinned.
The skin colors themselves are the result of a pigment called melanin. Melanin is produced by melanocytes, cells that reside in the skin’s top layer, or epidermis. There are two types of melanin: eumelanin, which produces a brown to black color,
and pheomelanin, which produces a red
to yellow color. Although melanin is the
The color of skin is determined by the amount of a photoprotective pigment called melanin. Melanin comes in two forms: pheomelanin and eumelanin. Individuals with a light complexion produce more pheomelanin and those with a dark complexion produce more eumelanin. The number and size of melanin particles vary among individuals, producing a vast range of skin tones.
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S k i n : T h e S c i e n c e I n s i d e
Our sense of touch comes from the nerve endings found in the dermis.
The subcutaneous tissue is the
bottom layer of skin and is mostly made up of fat. It also contains our skin’s nerves and blood vessels, as well as the roots of our oil and sweat glands and hair.
The top surface of the dermis and the bottom surface of the epidermis are covered with bumps that help them fit together like puzzle pieces. The patterns these bumps create are unique to each of us and make up our fingerprints and other lines on our skin.
A hair follicle is the tube-shaped sac that contains a hair. One hair grows out of each follicle and follicles are found throughout the body, except on the palms, soles, and lips.
These images show skin from different areas of the body. From left to right, they are from the palm or sole, the groin or armpit, and the rest of the body. The palm skin shows a much thicker epidermis (pale pink, top) than the others and is richly supplied with sensory nerves (yellow) in the dermis (dark pink). The skin from the groin shows a large hair arising from a follicle. A sebaceous gland (to the right of the hair) produces sebum, an oily substance which waterproofs the hai r . A c oiled sweat gland (blue) can also be seen leading to the skin’s surface through the hair’s shaft. The skin from other parts of the body has fewer sweat glands.
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Part 1: Skin Form and Function
Oil glands are known as seba-
ceous glands. They secrete an
oily substance called sebum, which helps skin and hair retain their moisture, protects them from friction, and acts as waterproofing. Oil glands are found all over our bodies, but are concentrated on the scalp, face, chest, and genitals.
Why do we have skin?
We all know that skin keeps us from seeing each other’s insides. But, really, what is it supposed to do? Skin has four main jobs:
PROTECTION: Our skin is our
first line of defense against infection. It keeps dirt, germs, and other harmful substances in the environment from getting to our insides.
Two types of sweat glands help
the body cool off. The eccrine
glands produce sweat when we’re hot, stressed, or experiencing strong emotions. They’re mostly found on our palms, soles, scalp,
and underarms. The apocrine glands develop during puberty
and produce sweat during times of stress or strong emotion. They’re mostly found under our arms and around nipples and genitals. Sweat is released from the lower layers of the skin through pores, or tiny holes in the skin.
It also keeps us from drying out. The oil produced in our sebaceous glands rises to the surface of our skin or hair and acts as a barrier so that only a certain amount of moisture can leave our bodies. Often our skin feels dry when too much oil is removed from the skin and moisture is allowed to escape from the body.
TEMPERATURE REGULATION:
Blood vessels in our skin expand and contract based on how warm or cold we are. When our body is hot, our blood vessels expand and bring warm blood closer to the surface of our skin, so that heat is released. Our sweat glands also make extra sweat so it can evaporate from the skin’s surface and cool us off. In this way, our skin acts like a built-in air conditioning unit.
In addition to containing all these things, the subcutaneous tissue also acts as a pillow to protect our internal organs from injury and holds in our body’s heat to keep us warm.
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S k i n : T h e S c i e n c e I n s i d e
When we’re cold, the opposite happens. The skin’s blood vessels narrow, trying to keep the warm blood away from the surface of the skin. The skin will become pale and cold, and body heat will move inward toward our organs.
We also may develop goose bumps. When the body gets cold (or excited), it causes the muscles attached to the base of each hair to pull it upright. This reflex, which all mammals and birds have, lets an animal warm up by trapping extra air closer to the skin so it can act as a warming layer. Animals also use this technique to make themselves look bigger to enemies. That’s why a cat looks bigger just before it gets into a fight with another animal, and why birds look fluffier when they’re sitting at a birdfeeder on a cold day. Goosebumps no longer serve a purpose for humans.
SENSATION: Nerves in our skin
send signals through the spinal cord to our brain about the things around us. This tells us about our surroundings, like whether we’re touching wet mud or hard rock. Nerves also protect us by warning us about what can hurt us, like really hot or sharp things.
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Part 1: Skin Form and Function
pain, and pressure (or touch) receptors. There are more pain nerve endings in our bodies than any other kind, which helps the body know where it is injured.
Other nerve endings in our skin lead to sexual excitement. These nerve endings stimulate the nervous and endocrine (hormonal) systems, which send messages to the brain and the sexual organs to “turn them on.” (Of course, all senses play a role in sexuality, as does the mind, and not every touch is arousing.)
HEALTH WARNINGS: The skin
can act as an early warning system to let us know that there’s something wrong elsewhere in the body. The skin’s texture, temperature, and color all give hints about our general health and when something is wrong elsewhere. For instance, if the skin is hot, then we may have a fever and be sick. A yellowish color to the skin may point to problems with our liver. An irregularly shaped brownish spot that suddenly appears even could point to skin cancer.
Nerve receptors are not evenly spaced throughout the body. Where they are closer together, we are more sensitive. They are furthest apart in the middle of the back. They are closest on our hands, lips, face, neck, tongue, and feet. In fact, each fingertip has about 100 touch receptors.
There are about 20 different kinds of nerve endings; the most common ones are heat, cold,
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S k i n : T h e S c i e n c e I n s i d e
The skin is one of the first defense mecha-
Skin and the Body’s Systems
nisms in your immune system. Your skin
has tiny glands that secrete sweat and oil. Those fluids help decrease the pH on the surface of your skin to help kill microorganisms. The enzymes in your sweat can digest bacteria.
The integumentary system consists of
the skin, hair, nails, glands, and receptors. Its main function is to act as a barrier to protect the body from the outside world. It also functions to retain body fluids, protect against disease, eliminate waste products, and regulate body temperature. In order to do these things, the integumentary system works with all the other systems of your body, each of which has a role to play in maintaining the internal conditions that a human body needs to function properly.
The skin works with the excretory system
by the removal of dead cells and sweat, which contains waste products. Skin also works to release waste, including water, salts, and urea, a toxic substance formed in the body’s production of energy. Waste travels through the sweat gland and out of the body through sweat pores, which are located in the epidermis.
The integumentary system has many functions, most of which are involved in protecting and regulating your body’s internal functions in a variety of ways:
By helping to synthesize and absorb vitamins A, D, E, and K, the integumentary sys-
tem works with the digestive system to
encourage the uptake of calcium from our diet. These substances enter the bloodstream though the capillary networks in the skin.
• Protects the body’s internal living tissues and organs